The Passport Office's claims that there is no backlog of travel documents in its offices was challenged on Tuesday night after photographs showed that hundreds of files, full of applications, have been stacked in a passport office room that is usually used for meetings.

The photographs, which were leaked to the Guardian, were taken in a second-floor conference room at the office's Liverpool branch on Tuesday, a source said. The room seems to have been hurriedly converted to store boxes of files. Staff say this is the first time that this room has been used to store files of applications, and it has forced them to hold meetings in a stationery cupboard.

Paul Pugh, the interim chief executive of the Passport Office, has maintained that there is no backlog of passports.

He said: "We have been experiencing exceptional early-summer demand for passports, in part due to the improving economy and a rise in holiday bookings.

"During this busy period we have processed more than 97% of straightforward passport renewal and child applications within the three-week target turnaround time.

"There is no backlog — over 99% of straightforward applications have been processed within four weeks."

Union officials say HM Passport Office is in crisis, with 500,000 cases waiting to be processed, and blame job cuts and office closures, which have left it unable to handle the rising level of demand. Labour and Tory MPs say they have received hundreds of complaints from constituents who claim to have suffered delays in their passport applications. The home affairs select committee has asked Pugh to give evidence on the delays next week.

The photographs show hundreds of boxes of orange and white files stacked on tables. A source close to the Liverpool office said that there were 15 to 20 applications in each box, and that the orange boxes were overseas applications while the white boxes showed those from the UK.

The room is usually used for meetings and induction sessions and is usually partitioned into two, the source said. This room was not used to store application files during the peak period last year and has not been used before for this purpose, according to the source.

Two other meeting rooms on the first floor of the building and another second-floor meeting room are also being used to house applications that are waiting to be processed, according to the source.Mark Serwotka, the head of the PCS union, whose members work in the office, said: "There are clearly very major problems in the Passport Office and there are simply not enough staff to cope with the applications that are coming in."

David Hanson, the shadow immigration minister, said the photographs would confirm the suspicions of many people who have tried to deal with the office in recent weeks, and called on the home secretary, Theresa May, to get a grip of the problem.

"Every picture tells a story and it is clear from constituency contact that passport cases are piling up across the country. The home secretary won't even admit there is a problem, let alone take action to deal with it.

"Even according to the government's own statistics, 90,000 passport cases haven't been dealt with on time this year, so there is simply overwhelming evidence that families across the country are suffering needless stress, anxiety and problems simply because of mismanagement at the Home Offfice."

A Home Office official has acknowledged that the stacked files contain applications for passports or renewals, and that they are being stored in a converted room because of an unprecedented demand for documentation.

However, the official said each file had been scanned into the system and was deemed to be "work in progress", which would be processed in the near future.